XMM-Newton Observation of GRB040827
- GRB040827 was discovered by INTEGRAL on August 27, 2004 at 11:50 UTC in the field of view of the IBIS telescope (Gotz et al. GCN2670).
- The notification arrived to VILSPA at 13:44 UTC, and following a quick evaluation, the GRB was approved by XMM-Newton Project Scientist for a ToO observation in revolution 864.
- The observation was started on 2004-08-27 at 18:07:56.UT under ObsId=0164570401, just 4 hrs 24 mins. after the notification of the burst, and lasting for a total of 54.3 ksec. The pointing coordinates were RA=15:16:57.7, Dec=-16:09:29.
- Already after the first 1000 sec of exposure, a source was clearly present in the pn image, within the expected error circle (Rodriguez-Pascual and Juarez GCN2678). Since this source was more than 1arcmin off the camera boresight, the telescope was re-pointed.
The EPIC-pn count rate of this source decreased from 0.06 counts/sec to 0.03 counts/sec in ~30ksec.
After a preliminary processing of the data, the centroid of this variable source is at RA=15:17:01.4, DEC=-16:08:30. A quick look inspection of the pn image indicates that the source may be extended.
- For the optical/NIR counterparts of GRB040827 the reader may go through the GCN circulars. We will just mention that the coordinates of the variable source above agree within 3arcsec with the position of one of the NIR sources detected with Magellan Baade 6.5-m telescope as reported in GCN2681 (and named XMM-2 in that circular). Later circulars ( GCN2683 and GCN2684) reported this source to fade by 0.5mag.
- The Observation Data File (ODF) will be available in the XSA here
- And the Pipeline Products will be available in the XSA here.
Quick analysis of preliminary XMM-Newton data
A minimum event filtering has been selected to generate these images; a further image filtering has been applied to enhance weak sources. The dashed circle shows the "aperture" used to generate the lightcurve and spectrum. Positions of NIR sources as reported in GCN2681 are marked with blue crosses.
PN light curve
PN light curve between 0.2 and 7 keV (background subtracted). After ~30ksec the count rate of the source decreased by a factor ~2.
We have fitted the pn spectrum of GRB040827 with a power law and galactic absorption. The Hydrogen column density obtained in the fit is ~3 1021 cm-2, higher than the galactic value of ~0.8 1021 cm-2 in this direction. The flux in the 2-10 keV band is approximately 10 -13 erg cm-2 s-1 for a power law photon index of 2.5.
A single absorbed power law may not be enough to fully describe the X-ray spectrum of GRB040827; some structure seems to be present in the residuals of the fit to such a simple model.